Eddy current separation of blanks for the automated destacking of aluminum sheet

ABSTRACT

A method of separating blanks from a stack includes positioning a magnetic field generator in a fixed location proximate a peripheral edge of an upper portion of the stack, activating the magnetic field generator such that eddy currents are generated and result in a force vector in a direction away from a top-most blank of the stack, and pushing a blank, or multiple blanks, immediately below the top-most blank away from the top-most blank by the eddy currents.

FIELD

The present disclosure relates to a material handling machine andmethod, and more particularly to an apparatus and a method forseparating blanks.

BACKGROUND

The statements in this section merely provide background informationrelated to the present disclosure and may not constitute prior art.

In a material forming operation, such as a stamping operation, a stackof blanks is generally positioned in proximity to a stamping press andautomatically fed into a stamping press by a material handling machine,such as a material handling robot. Tool and die surfaces of the stampingpress receive the blanks and form the blanks into a desired shape. Therobot includes an end-effector, which is moved to a position above thestack of blanks, grasps and lifts the uppermost blank from the stack,and feeds the uppermost blank into the stamping press.

To facilitate the grasping operation of the end-effector, the stack ofblanks may be de-stacked or separated before the end-effector grasps theuppermost blank. The typical de-stacking method is not suitable forhigh-volume manufacturing cycle time which requires automated, rapid,and robust blank de-stacking. If two or more blanks are picked up by therobot, the system experiences a disruption and stops the productionline, resulting in downtime of the manufacturing process.

Moreover, the typical de-stacking method is not suitable for picking upa variety of blank materials and of varying dimensions. For example, atypical de-stacking method that works with steel blanks may not workwith aluminum blanks.

These issues associated with de-stacking equipment relative to materialblanks, and the limitation of only certain materials being handled, areaddressed by the present disclosure.

SUMMARY

In one form, a method of separating a blank from a stack of blanks isprovided, which includes positioning a magnetic field generator in afixed location proximate a peripheral edge of an upper portion of thestack, activating the magnetic field generator such that eddy currentsare generated and result in a force vector in a direction away from atop-most blank, and pushing a blank, or multiple blanks, immediatelybelow the top-most blank away from the top-most blank by the eddycurrents.

In other features, the blanks are an aluminum alloy material, and themagnetic field generator is an electromagnet. The magnetic fieldgenerator is a rotating assembly of permanent magnets having alternatingnorth and south poles. The method further includes injecting air into aside of the stack as the individual blanks are separated by the eddycurrents, and moving the top-most blank to a subsequent manufacturingoperation. Only one sheet at a time is displaced by the magnetic fieldgenerator. A width of the blanks is between about 25 mm to about 3000mm, a length of the blanks is between about 25 mm to about 3000 mm, athickness of each blank is between about 0.5 mm to about 6.0 mm, and aheight of the stack of blanks is between about 1 mm to about 2000 mm.The gravitational direction is between 90 degrees and 75 degrees asmeasured from a normal face of a blank.

According to other features, the magnetic field generator includes apolyphase winding. The magnetic field generator is a rotating assemblyof permanent magnets having alternating north and south poles. Theapparatus may further include an air knife configured to inject air intothe stack as the blank is separated by the eddy currents, a transportmechanism configured to move the top-most blank to a subsequentmanufacturing operation, a controller configured to transmit signals tothe jig for translational movement, and a position sensor incommunication with the controller to transmit a position of the jig tothe controller. In one form, the transport mechanism includes aplurality of suction cups configured to hold the top-most blank of thestack, and a robot with an end effector to hold the stack of blanks.Advantageously, the stack of blanks is not injected with any current byway of physical contact. In one form, the eddy currents result in aforce vector in a direction between 90 degrees and 75 degrees asmeasured from a normal face of a blank.

Further areas of applicability will become apparent from the descriptionprovided herein. It should be understood that the description andspecific examples are intended for purposes of illustration only and arenot intended to limit the scope of the present disclosure.

BRIEF DESCRIPTION OF THE DRAWINGS

The present disclosure will become more fully understood from thedetailed description and the accompanying drawings, wherein:

FIG. 1 is a schematic view of an apparatus for separating a blank from astack of blanks constructed in accordance with the teachings of thepresent disclosure;

FIG. 2 is a schematic view of one form of a magnetic field generatoroperable with the apparatus of FIG. 1 according to the teachings of thepresent disclosure;

FIG. 3 is a schematic view of a stack of blanks and one variation of amagnetic field generator operable with the apparatus of FIG. 1 accordingto the teachings of the present disclosure;

FIG. 4 is a schematic view of a stack of blanks and another variation ofa magnetic field generator operable with the apparatus of FIG. 1according to the teachings of the present disclosure; and

FIG. 5 is a flow diagram of a method for separating blanks from a stackin accordance with the teachings of the present disclosure.

Corresponding reference numerals indicate corresponding parts throughoutthe several views of the drawings.

DETAILED DESCRIPTION

The following description is merely exemplary in nature and is notintended to limit the present disclosure, application, or uses.

Referring to FIG. 1, a material handling apparatus 10 for separating ablank from a stack of blanks and for moving the separated blank to adesired location in accordance with the teachings of the presentdisclosure is shown. The material handling apparatus 10 in one form isused as part of a stamping press (not shown) in a manufacturingoperation using conductive blanks, such as aluminum and steel alloys.Generally, the material handling apparatus 10 includes a transportmechanism, such as a robot 12, a fixed magnetic field generator 16, anoptional air knife 18, and a jig 20 for holding and supporting the stackof blanks 22.

The robot 12 may include a robot arm 13 and an end-effector 14 attachedto the robot arm 13. The end-effector 14 may include a plurality ofsuction cups supplied with a vacuum via a hose 15 such that theend-effector 14 applies a suction force and thereby securely grasps andmoves a separated blank from the stack of blanks 22. Alternatively, theend-effector 14 may include a multi-fingered gripper or any conventionalmeans that can grasp and move the separated blank. The separated blankis moved by the end-effector 14 and fed into a stamping press (notshown), with the robot arm 13 moving back and forth between the stampingpress and the stack of blanks 22 until all of the blanks in the stackhave been sequentially fed into the press. (Only portions of the robot12 are shown via a schematic inset 11 for illustrative simplicity).

As described in greater detail below, the magnetic field generator 16 isused to remove unwanted blank(s) stuck to a top-most blank 23 when thetop-most blank 23 is grasped by an end-effector 14 so that the top-mostblank 23 can be separated from the remaining blanks in the stack ofblanks 22 to avoid inadvertent separation of more than one blank by theend-effector 14. More specifically, the end-effector 14, with itssuction force, may grasp more than one blank from the stack of blanks 22at a time. The magnetic field generator 16 generates a repulsive force Fto push any unwanted blank(s) that are stuck to the top-most blank 23downward. The unwanted blanks that are stuck to the top-most blank 23can be further separated with the assistance of gravitational force G,rather than separating individual blanks as with conventional blankseparating equipment. Further, the individual blanks are not physicallytouched by any equipment/components of the material handling apparatus10.

Referring to FIG. 2, the magnetic field generator 16 in one form is asolenoid 17, which employs a polyphase winding to generate a moving(translating) magnetic field M and eddy currents 19, which produce theforce vector F that functions to separate an unwanted blank that isstuck to the top-most blank 23, from the top-most blank 23. In one form,the polyphase winding may be a three phase winding. The magnetic fieldgenerator 16 is fixed and is configured such that the force generated bythe eddy currents 19 pushes any unwanted blank that is stuck to thetop-most blank 23 downward as shown in FIG. 1, the separation of whichis further assisted by the gravitational force G. The direction of themagnetic force produced by the eddy currents 19 of the magnetic fieldgenerator 16 is determined by a charge and vector product of the chargevelocity and the magnetic field according to Equation 1:

F _(B) =qv×B  (Equation 1)

where:

F_(B)=magnetic force vector

q=charge

V=velocity vector of the charge

B=magnetic field vector

Accordingly, the magnetic field generator 16 is configured such that thedirection of the force of the eddy currents 19 to separate an unwantedblank from the top-most blank 23 is downward, in a gravitationaldirection G, as shown. The force F may be in the range of 5 lbs to 200lbs depending on the application, and may vary further from theseexemplary values.

The material handling apparatus 10 may optionally include a controller24 for actuating the jig 20 to move the stack of blanks 22 up and downalong a Z-direction. The controller 24 is configured to move the jig 20and position the stack of blanks 22 to a predetermined height relativeto the stationary magnetic field generator 16 for an optimum separationforce between the unwanted blank that is disposed immediately below thetop-most blank 23 from the top-most blank 23. The jig 20 moves the stackof blanks 22 from an elevated position and progressively upwardly alongthe Z-direction such that a peripheral edge of an upper portion of thestack is continually positioned proximate the fixed magnetic fieldgenerator 16. A position sensor 30 may be disposed at the jig 20 and incommunication with the controller 24 to transmit a signal correspondingto a position of the jig 20 to the controller 24.

Optionally, the air knife 18 is configured to inject air into the stackof blanks 22 as the top-most blank 23 is sucked by the end-effector 14and the blank immediately below the top-most blank 23 is separated fromthe top-most blank 23 by a repulsive force F resulting from the localeddy currents of the magnetic field generator 16. The robot 12 isconfigured to move the top-most blank 23, which has been separated fromthe stack of blanks 22, to a target site for a subsequent manufacturingoperations.

Referring to FIG. 3, another form of a magnetic field generator 16′ isshown that is disposed adjacent to the stack of blanks 22 and includes arotor 25 and a plurality of magnets 26, which are permanent magnets, toform a rotating assembly. Similarly, the magnetic field generator 16′does not contact the stack of the blanks 22. The plurality of magnets 26are arranged to extend in radial directions of the rotor 25 and arespaced apart in the circumferential direction of the rotor 25, withnorth (N) and south (S) poles alternately arranged.

Rotation of the magnets 26 with alternating polarities results in aconstantly changing magnetic field, which induces an eddy current in anearby conductor, i.e., within the edge of the blanks 22. A magneticforce is equal to the product of an electric current, a magnetic field,and a length of a given conductor, in this instance the blankimmediately below the top-most blank 23. The interaction between themagnetic field generated by the magnet field generator 16 and the eddycurrent in the blanks 22 generates an opposing repulsive force F betweenthe blanks 22 and the rotating magnets 22 that serves to move the edgeof the blank immediately below the top-most blank 23 away from thetop-most blank 23. The blank immediately below the top-most blank 23then falls due to gravity. The repulsive force F is in a directiondefining an angle θ relative to the front face of the blank 22, which isbetween 75° and 90° in one form of the present disclosure. The opposingrepulsive force F produces a targeted “blank fanning” effect in whichthe generated magnetic force is produced in a controlled and targetedmanner to separate the blanks 22.

The magnitude of the opposing repulsive force F depends on therotational speed of the rotor 25, the magnetic field strength of themagnets 26, and the diameter of the rotor 25. Therefore, the repulsiveforce F resulting from the eddy currents and the magnetic field may becarefully tuned according to the specifications of the blanks 22 (e.g.,size, thickness, material).

Referring to FIG. 4, another variant of the magnetic generator 16″constructed in accordance with the teaching of the present disclosureincludes an inclined surface 42 facing edges of the stack of blanks 22,and an array of electromagnets 44 mounted along the inclined surface 42and disposed in close proximity to the edge of the blanks 22. Similarly,the magnetic field generator 16″ does not contact the edges of the stackof blanks 22. The array of electromagnets 44 are computer-controlled andare operable to induce eddy currents within the edges of the blanks 22by changing the magnetic field generated by the array of electromagnets44. The computer (not shown) controls the array of the electromagnets 44such that the electromagnetic field moves in reference to the edge ofthe blanks 22, thereby generating an opposing repulsive force F betweenthe blanks 22 and the array of electromagnets 44. The electromagneticfield moves at an angle θ between 90 and 75 degrees relative to thefront face of the blanks 22. The opposing repulsive force F in the blankedge serves to push down the blank that is disposed immediately belowthe top-most blank. Again, the unwanted blank immediately below thetop-most blank 23 is pushed down, in a gravitational direction. Thisfeature is one among several that distinguishes the teachings of thepresent disclosure from those of the prior art. Further, the materialhanding apparatus 10 and various forms of magnetic field generators16/16′/16″ advantageously do not inject any current by way of physicalcontact into the stack of blanks 22, which results in a simpler and moreefficient operation to separate and move blanks throughout variousmanufacturing operations such as stamping.

Referring now to FIG. 5, a method 50 of separating a blank from a stackof blanks 22 and moving a separated blank to a target site starts withpositioning a magnetic field generator 16 in a fixed location proximatea peripheral edge of an upper portion of the stack in step 52. Atop-most blank is lifted by, for example, an end-effector in step 54.The magnetic field generator is activated such that eddy currents and amagnetic force vector (i.e., a repulsive force) in a gravitationaldirection away from the top-most blank 23 are generated in step 56. Inone form, the gravitational direction is between 90 degrees and 75degrees as measured from a front face of a blank, and as illustrated inFIGS. 2 and 3. Therefore, an unwanted blank that is stuck to thetop-most blank 23 is moved away from the top-most blank 23 in thegravitational direction in step 58. Concurrently and optionally, air maybe injected into the stack as individual blanks are separated by therepulsive force resulting from the eddy currents. Finally, the top-mostblank 23 that is separated from the stack is moved to a subsequentmanufacturing operation, which may be by the robot 12 shown in FIG. 1 instep 60.

The blanks 22 may be any conductive materials where eddy currents can beinduced, such as aluminum alloys and steel alloys. In one form ofhigh-volume automotive production, a width of the blanks is betweenabout 25 mm to about 3000 mm, a length of the blanks is between about 25mm to about 300 mm, a thickness of each blank is between about 0.5 mm toabout 6.0 mm, and a height of the stack of blanks is between about 6 mmto about 2000 mm.

The apparatus and the method of the present disclosure are intended toeliminate the need for compressed air, dimple patterns, or other typicalmethods to facilitate separation of the blanks in stamping or otheroperations.

The description of the disclosure is merely exemplary in nature and,thus, variations that do not depart from the substance of the disclosureare intended to be within the scope of the disclosure. Such variationsare not to be regarded as a departure from the spirit and scope of thedisclosure.

1. A method of separating a blank from a stack of blanks comprising:positioning a magnetic field generator in a fixed location proximate aperipheral edge of an upper portion of the stack; activating themagnetic field generator such that eddy currents are generated andresult in a force vector in a direction away from a top-most blank; andpushing, by the magnetic field generator, at least one blank immediatelybelow the top-most blank away from the top-most blank after the top-mostblank is lifted by an external device, wherein the magnetic fieldgenerator is disposed relative to the stack in a way such that the forcevector is applied on the at least one blank to separate the at least oneblank from the top-most blank before the top-most blank and the at leastone blank are completely separated from remaining blanks of the stack.2. The method according to claim 1, wherein the blanks are an aluminumalloy material.
 3. The method according to claim 1, wherein the magneticfield generator is an electromagnet.
 4. The method according to claim 1,wherein the magnetic field generator is a rotating assembly of permanentmagnets having alternating north and south poles.
 5. The methodaccording to claim 1 further comprising injecting air into a side of thestack as the individual blanks are separated by the eddy currents. 6.The method according to claim 1, wherein a width of the blanks isbetween about 25 mm to about 3000 mm, a length of the blanks is betweenabout 25 mm to about 3000 mm, a thickness of each blank is between about0.5 mm to about 6.0 mm, and a height of the stack of blanks is betweenabout 1 mm to about 2000 mm.
 7. The method according to claim 1 furthercomprising a step of moving the top-most blank to a subsequentmanufacturing operation.
 8. The method according to claim 1, whereinonly one sheet at a time is displaced by the magnetic field generator.9. The method according to claim 1, wherein the gravitational directionis between 90 degrees and 75 degrees as measured from a normal face of ablank.
 10. An apparatus for separating blanks from a stack comprising: afixed magnetic field generator; a jig configured to hold and translatethe stack of blanks past the fixed magnetic generator such that aperipheral edge of an upper portion of the stack is continuallypositioned proximate the fixed magnetic field generator; and a positionsensor for detecting a position of the jig, wherein eddy currents fromthe fixed magnetic field generator force an unwanted blank immediatelybelow a top-most blank of the stack to be separated from the top-mostblank of the stack and to fall with gravity after the top-most blank islifted by an external device, and wherein the fixed magnetic fieldgenerator is disposed relative to the stack in a way such that the eddycurrents separate the unwanted blank from the top-most blank before thetop-most blank and the unwanted blank are completely separated fromremaining blanks of the stack.
 11. The apparatus according to claim 10,wherein the magnetic field generator includes a polyphase winding. 12.The apparatus according to claim 10, wherein the magnetic fieldgenerator is a rotating assembly of permanent magnets having alternatingnorth and south poles.
 13. The apparatus according to claim 10 furthercomprising an air knife configured to inject air into the stack as theunwanted blank is separated by the eddy currents.
 14. The apparatusaccording to claim 10 further comprising a transport mechanismconfigured to move the top-most blank to a subsequent manufacturingoperation.
 15. The apparatus according to claim 14, wherein thetransport mechanism comprises a plurality of suction cups configured tohold the top-most blank of the stack.
 16. The apparatus according toclaim 14, wherein the transport mechanism comprises a robot with an endeffector to hold the stack of blanks.
 17. The apparatus according toclaim 10 further comprising a controller configured to transmit signalsto the jig for translational movement.
 18. The apparatus according toclaim 17, wherein the position sensor is in communication with thecontroller to transmit the position of the jig to the controller. 19.The apparatus according to claim 10, wherein the stack of blanks is notinjected with any current by way of physical contact.
 20. The apparatusaccording to claim 10 wherein the eddy currents result in a force vectorin a direction between 90 degrees and 75 degrees as measured from anormal face of a blank.